1. Field of the Invention
The present invention relates to an active delay method which is capable of synchronizing a binaural hearing device stably by reducing a time difference which may be produced due to wireless connection of two hearing devices, and a wireless binaural hearing device using the same method.
2. Description of the Related Art
In recent years, approaches have been frequently researched which uses a binaural hearing device to strengthen user's hearing. A binaural hearing device is a device which processes signals acquired through two or more hearing devices or microphones attached to ears or a neck and transfers the processed signals to user's ears. Use of the binaural hearing device can improve user's hearing and allows the user to detect a position of a sound source reliably.
However, existing hearing devices have to be equipped with several microphones connected to each other by wires, which detracts from the beauty.
To avoid such a demerit, many attempts to transmit signals of a binaural hearing device by wireless have been made. Such attempts have focused on a wireless transmission system which can transmit signals acquired by one hearing device to another hearing device.
However, such a wireless transmission system cannot avoid producing a signal delay for signal modulation-demodulation and verification, as compared to a wired transmission system. General wireless systems may be used with no problem since they recognize a sound source to be just a little apart from them even if a time delay of 10 to 50 ms is produced. However, for a binaural algorithm, a delay measured in microphones is a very important factor as shown in FIG. 1. If a sound source is in front of two microphones, time of input of a signal in the left microphone is equal to time of input of the signal in the right microphone. However, if the sound is in the left side, the signal is measured in the left microphone and then, after a certain period of time, the signal is input to the right microphone. Therefore, the existing wireless binaural hearing devices have been designed to use this signal delay to improve user's hearing.
However, such wireless binaural hearing devices require wireless transmission time of about 10 to 50 ms, which may result in low sound recognition. FIG. 2 is a schematic view showing variation of a position of a sound source in the presence of a wireless binaural hearing device. If the sound source lies in front of the wireless binaural hearing device, a signal from the sound source arrives at both hearing devices in equal time. When the signal is transmitted to both binaural hearing devices by wireless in this manner, there occurs a signal delay, which makes a user feel as if the position of the sound source is shifted to the left or right side. For example, if the signal enters the left hearing device by a wire and data are transmitted to the right hearing device by wireless, the left hearing device may create an illusion that the sound source is in the left side. In the reverse case, the left hearing device may create an illusion that the sound source is in the right side.